1. Field
The present invention relates to an AC LED lighting apparatus using a voltage edge detector, and more particularly, to an AC LED lighting apparatus using a voltage edge detector, which is capable of detecting a rising or falling slope of a sine wave signal (for example, a rectified voltage (Vrec)) by using a voltage edge detector, and sequentially driving the AC LED lighting apparatus and controlling a serial/parallel is connection relationship among a plurality of LED groups according to the detected slope.
2. Discussion of the Background
A light emitting diode (LED) is a semiconductor element that is made of a material such as gallium (Ga), phosphorus (P), arsenic (As), indium (In), nitrogen (N), and aluminum (Al). The LED has a diode characteristic and emits red light, green light, or yellow light when a current flows therethrough. Compared with a bulb or lamp, the LED has a long lifespan, a fast response speed (time until light is emitted after a current flows), and low power consumption. Due to these advantages, the LED has tended to be widely used.
In general, a light emitting element could be driven only at a DC voltage due to the diode characteristic. Therefore, a light emitting device using a conventional light emitting element is restrictive in use and must include a separate circuit, such as SMPS, so as to use an AC voltage that has been currently used at home. Consequently, the circuit of the light emitting device becomes complicated and the manufacturing cost of the light emitting device increases.
In order to solve these problems, much research has been conducted on a light emitting element that can also be driven at an AC voltage by connecting a plurality of light emitting cells in series or in parallel.
FIG. 1 is a block diagram illustrating a configuration of a conventional AC LED lighting apparatus, and FIG. 2 is a waveform diagram illustrating waveforms of a rectified voltage and an LED driving current in the conventional AC LED lighting apparatus illustrated in FIG. 1.
As illustrated in FIG. 1, the conventional AC LED lighting apparatus includes an AC power source VAC, a rectification unit 10, a first light emitting group 20, a second light emitting group 22, a third light emitting group 24, a fourth light emitting group 26, a driving control unit 40, a first light emitting group driving unit SW1, a second light emitting group driving unit SW2, a third light emitting group driving unit SW3, and a fourth light emitting group driving unit SW4. Specifically, the rectification unit 10 receives an AC voltage from the AC power supply VAC and performs a full-wave rectification on the AC voltage to output a rectified voltage Vrec. The first light emitting group 20, the second light emitting group 22, the third light emitting group 24, and the fourth light emitting group 26 receive the rectified voltage Vrec and are sequentially driven. The driving control unit 40 controls the sequential driving of the first light emitting group 20, the second light emitting group 22, the third light emitting group 24, and the fourth light emitting group 26 according to a voltage level of the rectified voltage Vrec. The first light emitting group driving unit SW1, the second light emitting group driving unit SW2, the third light emitting group driving unit SW3, and the fourth light emitting group driving unit SW4 have a switching function and a constant current control function.
A process of driving the conventional AC LED lighting apparatus will be described below with reference to FIG. 2. The driving control unit 40 determines the voltage level of the rectified voltage Vrec applied from the rectification unit 10, and sequentially drives the first light emitting group 20, the second light emitting group 22, the third light emitting group 24, and the fourth light emitting group 26 according to the determined voltage level of the rectified voltage Vrec.
Accordingly, in periods during which the voltage level of the rectified voltage Vrec is equal to or higher than a first threshold voltage VTH1 and lower than a second threshold voltage VTH2 (t1 to t2 and t7 to t8 in one cycle of the rectified voltage Vrec), the driving control unit 40 maintains the first switch SW1 in a turned-on state and maintains the second switch SW2, the third switch SW3, and the fourth switch SW4 in a turned-off state, so that only the first light emitting group 20 is driven. In addition, in periods during which the voltage level of the rectified voltage Vrec is equal to or higher than the second threshold voltage VTH2 and lower than a third threshold voltage VTH3 (t2 to t3 and t6 to t7 in one cycle of the rectified voltage Vrec), the driving control unit 40 maintains the second switch SW2 in a turned-on state and maintains the first switch SW1, the third switch SW3, and the fourth switch SW4 in a turned-off state, so that only the first light emitting group 20 and the second light emitting group 22 are driven.
In addition, in periods during which the voltage level of the rectified voltage Vrec is equal to or higher than the third threshold voltage VTH3 and lower than a fourth threshold voltage VTH4 (t3 to t4 and t5 to t6 in one cycle of the rectified voltage Vrec), the driving control unit 40 maintains the third switch SW3 in a turned-on state and maintains the first switch SW1, the second switch SW3, and the fourth switch SW4 in a turned-off state, so that the first light emitting group 20, the second light emitting group 22, and the third light emitting group 24 are driven.
In addition, in periods during which the voltage level of the rectified voltage Vrec is higher than the fourth threshold voltage VTH4 (t4 to t5 in one cycle of the rectified voltage Vrec), the driving control unit 40 maintains the fourth switch SW4 in a turned-on state and maintains the first switch SW1, the second switch SW2, and the is third switch SW3 in a turned-off state, so that all of the first light emitting group 20, the second light emitting group 22, the third light emitting group 24, and the fourth light emitting group 26 are driven. However, in the conventional AC LED lighting apparatus described above, when the AC voltage is applied, a rising or falling slope of a sine wave signal is changed with time according to the magnitude of the AC voltage signal, and thus, the moment at which the switches are switched for the sequential driving is changed. Therefore, when the slope of the sine wave signal is large (that is, the magnitude of the input voltage increases), the LED is turned on earlier. When the magnitude of the input voltage is small, the LED is switched later, so that a current flows for a short time, that is, a turn-on time is shortened. Therefore, power consumption is irregularly decreased. As a result, when the conventional AC LED lighting apparatus is used, the switching time of the LED is generally changed according to the magnitude of the input voltage, making it difficult to maintain constant power. Furthermore, the conventional AC LED lighting apparatus includes a plurality of LED arrays, and sequentially turns on and off the plurality of light emitting groups according to the voltage level of the rectified voltage. Thus, since the light emission periods of the respective light emitting groups are different, the optical uniformity of the AC LED lighting apparatus is degraded and the lifespan of the plurality of light emitting groups becomes different. Consequently, the AC LED lighting apparatus is dependent on the LED array with the light emission period having the long lifespan.